Conventionally, a styrene-based resin has been widely used in household electric appliances, business machines, household utensils, food containers, packaging materials, toys and others for the reason that it is well balanced in price, transparency, mechanical strength, and formability. Also, it is possible to make a styrene-based resin through diverse methods and in general, and it is molded by means of injection molding, extrusion molding, blow molding, vacuum molding, or injection molding etc. The styrene-based resin is mainly produced by thermal polymerization or radical polymerization method, which latter makes use of an initiator. Typical manufacturing processes of it are bulk polymerization method and suspension polymerization method, and the former is more popular for the reasons of smaller product contamination with impurities such as dispersant, and lower cost with advantage.
A styrene monomer which becomes a raw material for a styrene-based resin is used as a starting material for various synthetic resins as well, and as such is an industrially important monomer. For example, in the field of electrophotography, it is used as a binding resin for toner, for example: polystyrene; poly-p-chlorostyrene; polyvinyl toluene; styrene-p-chlorostyrene copolymer; styrene-vinyl toluene copolymer; styrene-vinylnaphthalene copolymer; styrene-acrylic acid ester copolymer; styrene-methacrylic acid ester copolymer; styrene-α-chloromethacrylic acid methyl copolymer; styrene-acrylonitrile copolymer; styrene-vinylmethylether copolymer; styrene-vinylethylether copolymer; styrene-vinylmethyl ketone copolymer; styrene-butadiene copolymer; styrene-isoprene copolymer; styrene-acrylonitrile-indene copolymer; and a styrene-based copolymer which is made through a reaction between a styrene monomer and a comonomer selected from acrylamide, vinyl chloride, vinyl acetate, vinyl benzonate, ethylene, propylene, butylene, vinyl methyl ether, and vinyl isobutyl ether.
A toner for electrophotography is pre-added with a charge control agent for the purposes of increasing a rising speed of charging of the toner, improving the charging characteristics through sufficient charging of the toner and thereby properly controlling and stabilizing a electric charge amount, and increasing the rate of development of the electrostatic latent charge to thereby forming a clear image. Examples of the currently known charge control agent in the field of the technology in issue include, as negatively chargeable charge control agents, a metallic complex salt of mono azo dye, a metallic complex salt of hydroxyl carboxylic acid or dicarboxylic acid or an aromatic diol, and a resin containing an acidic component. Examples of the currently known positively chargeable charge control agents include nigrosine dyes, azine dyes, triphenylmethane-based dyes, quarternary ammonium salt, and polymers having quarternary ammonium salt on a side chain thereof. With respect to the above-named charge control agents, there is a room for improvement against the problems such as a difficulty in balancing between the image density and fogging, a difficulty in attaining a sufficient image density under a high humidity condition, a poor dispersion in the resin, and harmful effects imparted to the preservation stability, the fixity, and the anti-offset characteristic.
As a trial for attaining such improvements, there have been efforts made to improve the compatibility to the toner resin and to use a resin having charge control property as the toner for electrostatic charge image developing. For example, in Patent Document 1 there is described a toner for electrostatic charge image developing, which contains as the charge control agent a condensate of a salicylic acid having a substituent. Also, Patent Document 2 describes a toner for electrostatic charge image developing, which contains at least a salicylic acid resin. In addition, in Patent Document 3 there is described a toner for electrostatic charge image developing which contains a copolymer consisting at least of a styrene derivative and a styrene derivative having a carboxyl group and a hydroxyl group. Furthermore, Patent Document 4 describes a negatively chargeable toner containing a negatively chargeable charge control agent which consists of a polymer from a polymerizable composition containing a radical polymerizable monomer having a diphenyl group which may be substituted with a carboxyl group. Also, Patent Document 5 describes a negatively chargeable toner for electrophotography containing a charge control agent in an amount of 0.1 through 10 weight parts against 100 weight parts of a binder, wherein the charge control agent, represented by a particular chemical formula, consists of 1 through 30 weight % of sulfoalkyl(meth)acrylic acid monomers and 99 through 70 weight % of other vinyl type monomers which are capable of forming a copolymer with the former. Then, Patent Document 6 describes a toner for electrostatic image development containing a charge control agent which is a copolymer having a sulfonic acid group and which is obtained through a copolymerization among a vinyl aromatic carbon hydride and a (meth)acrylate and a sulfonic acid group-containing (meth)acrylamide, in which the copolymerization rate of the sulfonic acid group-containing (meth)acrylamide is 0.1-1.8 weight % and a weight average molecular weight of the copolymer is 2,000-15,000.
In recent years, there have been made improvements in performances of copiers and printers so that a higher resolution in the images provided by the copiers and printers are attained among other things, and also there has been an expansion of system such as electrophotography system including ones for low speed developing as well as those for high speed developing. It has been also desired to develop such a charge control agent that is designed to enable a better control of the charge risen up of the toner, to exhibit more excellent charging characteristics, to enable a formation of a clear and high resolution image, and to be manufactured with simplicity. Also, a good charge control agent has been demanded which can be used as a powdery paint, which is employed in electrostatic powder coating wherein an electrostatically charged powdery paint is adsorbed to the surface of a structure by the electric charge thereof and is burnt thereon.